Photosensitized degradation of paracetamol by rose bengal-modified clays and alginate materials/rose-bengal

YANET MAYER; CAROLINA WAIMAN; WALTER MASSAD; JOSÉ NATERA; GRACIELA ZANINI

Wuhan-Modalidad Virtual

Conferencia; The 11th International Conference on Interfaces Against Pollution (IAP2021); 2021

Huazhong Agricultural University (HZAU)

The presence of contaminants in natural waters (ground and surface waters) and their accumulation inplants and animals is a worldwide major concern. Among the large variety of substances that humanactivity introduces into the environment are organic pollutants. Within this group, pharmaceuticals arethe ones that have given rise to most concern and studies in recent years. Just in the EU, the use ofsome pharmaceutical products, such as paracetamol, is estimated to be similar to the pesticidesamount. Paracetamol is a widespread painkiller and antipyretic drug which is widely consumedthroughout the world. Nowadays, it is one of the most frequently found drugs in hospital effluents, watertreatment plants, rivers and sludge. Therefore, removing and/or degrading this contaminant in aqueousmedia is of great interest since clean water is essential for life. In this context, photosensitizeddegradation is an environmentally friendly option for organic pollutant removal. These processes aremostly based on the use of a photosensitizer that absorbs ultraviolet or visible radiation and reacts withwater-dissolved molecular oxygen generating reactive oxygen species (ROS). Subsequently, ROS areresponsible for degrading organic compounds dissolved in water. Rose bengal (RB) is a non-toxic dyethat can be used as photosensitizer. It is known that RB dissolved in water photogenerates singletoxygen (O2(1Δg)), a type of ROS [1]. Probably, the main challenge of photosensitized degradationprocesses is to remove the photosensitizer from water at the end of the photo oxidative cycle. Thisinconvenience can be solved by incorporating this substance in an easy-to-handle green supportwithout losing its photochemical properties and allowing easy separation. This work aims to synthesizematerials composed by RB, montmorillonite clay (MMT) modified with aminopropyltriethoxysilane(APTES) and alginate biopolymer for the formation of MMT-APTES-RB beads in order to generateO2(1Δg) and then photodegrade paracetamol in water.The ability of the synthesized beads to photogenerate ROS was studied by oxygen uptake experiments.For this purpose, ground-state oxygen consumption (O2(3Σg-)) was determined using a specificelectrode and a furfuryl alcohol solution (1×10-4M) as substrate for O2(3Σg-) variation recording. Afterdetermining that the beads are capable of photochemically generating O2(1Δg), photodegradationassays of paracetamol were performed. These experiments were carried out with irradiation at awavelength between 500 and 550 nm (green LED) in the presence and absence of MMT-APTES-RBbeads under constant stirring. In addition, the adsorption of the contaminant on the beads was studiedin the dark. The assays were performed with a paracetamol solution (1×10-4M) at a pH above its pKaso that the phenolic group is deprotonated and reactive towards O2(1Δg). UV-Vis spectra ofparacetamol were recorded every 10 min for 90 min. The spectraof the studies in the presence of beads in the dark and those of direct photolysis (irradiation in theabsence of beads) showed no variation over time. On the other hand, spectra collected duringexperiment of irradiation in presence of beads showed spectral changes (decrease in absorbance andappearance of new bands) indicating that paracetamol is degrading and new species are being formed.Results in the present study demonstrate that the synthesized material can photogenerate O2(1Δg) inaqueous solution and this ROS is capable to photodegrade paracetamol dissolved in water. In addition,no quantifiable adsorption of the pharmaceutical was observed on the bead. Photodegradation of thiscontaminant by direct irradiation was not observed.In addition to the ability to generate O2(1Δg) and degrade organic contaminants dissolved in water,these materials are economical and environmentally friendly because their components are non-toxicand because their synthesis does not involve toxic solvents and does not generates waste. Finally, it isalso important to point out that these beads are easy to handle, so they can be effortless removed fromaqueous media. These features enable MMT-APTES-RB beads to be proposed as waterdecontamination materials from emerging contaminants such as paracetamol.References[1] C. R. Lambert and I. E. Kochevar, ?Does rose bengal triplet generate superoxide anion?,? J. Am.Chem. Soc., vol. 118, no. 13, pp. 3297?3298, Apr. 1996.